Incandescent lamp



Filed Jan. 31, 1957 FIG.2.V

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INVENTOR. J A CK MARTIN United States Patent() INCANDESCENT LAMP JackMartin, Paramus, N.J., assignor to Westinghouse Electric Corporation,East Pittsburgh, Pa., a corporation of Pennsylvania Application January31, 1957, Serial No. 637,447 "3 Claims. (Cl. 313-271) As presentlymanufactured virtually all the incandescible elements employed inelectric lamps are of the coiled variety wherein a long strand ofrefractory metal wire, such as tungsten, is wound in the form of a helixto provide a coiled filament having a plurality of accurately formed andspaced turns. In order to facilitate connecting the filament with thelamp lead wires a seg- 1 ment of uncoiled wire is usually left at eachend of the filament to provide generally straight end sections orso-called coil legs.

It has been the standard practice in the industry when mounting lampfilaments of the foregoing character to permit the end sections or legsof the coil to retain their substantially straight-line transverserelationship with the mount axis and lead wires which relationship isintroduced during the mounting operation in order to facilitate theattachment of the filament to the leads. art mounting is illustrated inFig. 3 and it will be observed that with the coil legs in thistransverse position the adjoining unsupported coiled body portions ofthe filament Another object of theinvention is to provide a method formounting a filamentary light source whereby the end portions of thelight source adjacent their points of anchorage are automaticallyrendered more rigid and less susceptible to the deteriorating effects ofmechanical forces. i a a The foregoing objects and others which willbecome obvious to those skilled in the art as the description proceedsare achieved byadjusting the filament after it has been mounted on thelamp lead wires so that its end sections inward of the leads are bowedoutwardly in a manner such that the adjoining body portions of thefilament are permanently strained and rigidified.

A better understanding of the invention may be obtained by referring tothe accompanying drawing in which like numerals of reference indicatesimilar parts throughout the several views, wherein:

1 Fig. 1 is a perspective view of an incandescent lamp including as apart thereof the improved filament mount structure of this invention;-

Fig. 2 is a front elevational view on an enlarged scale of the filamentmount employed in the lamp shown in Fig. 1 and illustrates more clearlythe configuration of the filament according to the invention;

Fig. 3 is a view of a filament mount similar to that illustrated in Fig.2 but shows the prior art mode of mounting the filament on the leadwires;

Figs. 4 and 5 are enlarged fragmentary views of one of the filament-leadwire junctions employed in the mount shown in Fig. 2 and illustrate ingreater detail the spatial relation between the leads and various partsThe prior proper are relaxed, so to speak, and hence easily influencedby and responsive to gravitational or other mechanical forces.Consequently, when the filament is heated to its operation temperatureand the wire expands and becomes more pliable, these unsupportedportions tend to sag and, should the lamp be subjected to vibration orsudden impacts, develop a pronounced whip-like motion or sympatheticallyvibrate at their resonant frequencies or at harmonics thereof resultingin the permanent deformation and progressive deterioration of the coil.The rate of deterioration increases as the unsupported sections of thefilament are stretched and lengthened until the wire breaks or the coilbecomes so badly entangled that segments are shorted out thus reducingthe lighted length of the filament and increasing its temperature andvaporization rate. In either case, the filament is quickly renderedinoperative causing premature failure of the lamp.

It is accordingly the general object of this invention to provide anincandescent lamp which will have a longer useful life under adverseoperating conditions.

Another object of the invention is to provide a filament mountconstruction for incandescent lamps wherein unsupported portions of thefilament are rigidified and better able to withstand the deterioratingeffects of mechanical forces normally encountered during the usage ofthe lamp.

A further and more specific object of the invention is to improve thehot shock and vibration strength of a coiled filament by minimizing theelfect of the sag and vibratory movement induced therein by mechanicalforces encountered during operation of the lamp.

of the filament before and after the adjustment of the filament,respectively, and the manner of effecting such adjustment according tothe invention;

Fig. 6 is a graphic representation of comparative test results obtainedon lamps manufactured according to the prior art construction versusthose incorporating the present invention illustrating the mortalityrate of each lamp type when subjected to physical shock duringoperation;

Figs. 7, 8 and 9 are alternative embodiments illustrating the manner inwhich the invention may be incorporated in various types of mountassemblies and structures.

Although the principles of this invention are broadly applicable toother types of electrical devices wherein the gradual deterioration of afilamentary element is efiected by gravitational or other forces orwhere additional strengthening of such an element is desired, theinvention is especially suited for use in miniature type lampsincorporating coiled filaments having unsupported sections ofconsiderable length and hence has been so illustrated and will .be sodescribed.

Referring now to the drawing, in Fig. 1 there is illustrated a miniatureincandescent lamp 10 comprising gen erally a light-transmitting envelope12 having sealed therein a mount assembly 16 upon which an elongatedincandescible element 24, suchas a coiled filament of tungsten or othersuitable refractory metal wire, is mounted and arranged in accordancewith the principles of this invention. In order to facilitate electricalconnection of the lamp 10 with a source of electrical energy a basemember 14, such as the bayonet type illustrated, is provided anddependingly secured to the sealed end portion of the envelope 12 in thecustomary manner.

As particularly shown in Fig. 2, the mount assembly 16 comprises a pairof lead wires 20 and 22 held in spaced relation by a body of insulatingmaterial 18, such as a glass bead, which is fused to andspansintermediate portions of the said lead wires. The filament 24 is mountedon the end portions of the lead wires 20 and 22 and may be convenientlymaintained in the desired configuration, such as the inverted V orso-called 02V shape shown in Fig. 2, by an elongated supportits loopedend portion supportingly engages an inter.

mediate part of the filament. The coiledfila'ment 24 is desirablyprovided with generally straight end sections or legs 28 of uncoiledwire which serve tofacilitaltethe attachment of the filament 24 to thelead Wires 20 and '22.

In mounting the filament 24 according to the invention, each of its endsections 28 are first secured as by clamping or other suitable means tothe ends of the lead wires 20 and 22 in transverse relation therewithandthe filament proper draped over the looped end of the supporting member26' in accordance with the present mounting practice so that thefilament 24 is arranged in a generally straight-sided inverted V as inthe prior art mount 30 shown in Fig. 3. The portions of the end sections28 inward of and remote from the leads Z and 22 are then fiaredor b'entupwardly from their as-mounted straight-line transverse relation withthe mount and lead wire axes by means of a suitably actuated formingmember 52 in the' manner illustrated in Figs. 4 and 5, respectively; Themovement and orientation of the forming member 52 are such that itcontacts the end sections 28 at a point inward of and remote from theleads 20 and 22, preferably at a point adjacent the coiled portion ofthe filament 24 (see Fig.

4). The upward thrust of the member 52 is of suificient magnitude thatthe sections 28 are permanently deformed with a wiping action so thatthe aforementioned parts of the filament end sections 28 are inclined orflared outwardly from each other and the mount axis toward parallelismwith the connecting ends of the lead wires 20 and 22, as illustrated inFigs. 2 and 5. With the end sections 28 deformed inthis manner theadjoining unsupported segments of the coiled body portion of thefilament 24 are strained and bowed outwardly so that in its finallyadjusted condition the filament 24 has the arch-like configurationdepicted in Fig. 2. It should be noted that with the foregoingarrangement the parts of the end sections 28 adjacent the main bodyportion of the filament 24 are wiped by the forming member 52 so thatinstead of the sections 28 being sharply bent at the inward edges of thelead wires 20 and 22 they are gradually bent at a point remote from theleads thereby minimizing the stress imparted to the filamentary materialand the danger of fracturing the filament wire during the formingoperation. In practice the wiping action effected by the forming member52 may be accomplished by a pair of tweezers, which are manipulated tosuitably deform and adjust the filarnent end sections 28.

By virtue of its permanently strained condition and arch-likeconfiguration the main body portion of the filament 24 is rigidified andits mechanical strength materially improved in much the same manner asthe rib members and the covering material of an umbrella are stifienedand form a rigid structure when locked in their expanded or openedposition. Hence, should the lamp be subsequentlysubjected'to vibrationalor other destructive forces, particularly during operation when thefilament 24 is in a hot pliable condition, the gradual collapse anddeterioration of the unsupported end spans of the coiled portionnormally produced by such forces will be retarded inasmuch as the upwardthrust and rigidifying effect derived from the strain pattern and shapeimparted to the filament must first be overcome and neutralized, so tospeak. Continued use of the lamp .110 under such adverse operatingconditions will, of course, eventually cause the filament 24 togradually assume its normal shape and strain-free condition where- 7upon it will deteriorate in substantially the same manner andatthe samerate as heretofore.

It is also a significant feature of the invention that the rigidifyingand strengthening effect obtained from the foregoing adjustment of themounted filament 24 will be especially long-lived by virtue of the factthat the deformation which produces the effect is confined to the endsections 28 which, because of the cooling effect of the adjoining leadwires 20 and 22, operate at the lowest temperature and are the leastpliable or yieldable parts of the filament structure considered as awhole.

In the prior art type mount assembly 30 illustrated in Fig. 3, while thelead wires 32 and 34, support member 38, insulator 36, and filament 40are substantially the same with respect to structure and spatialrelationship as those employed in the improved mount 16 embodying theabove-described principles of the invention, the end portions 42 of thefilament 40 were permitted to retain their as-mounted transverserelation with the mount and lead wire axes so that the adjoining coiledportions of the filament 40 were substantially straight and in a relaxedcondition. With this arrangement the expansion and pliability of thefilament 40 incident with the operationof the lamp'soon caused theunsupported sections of the coil to sag inwardly toward each other andthe support 38 and by virtue of the proximity of the parts would, in avery short period of time, result in entanglements and short circuitswhich rendered the lamp virtually useless ifnot totally inoperative.

. Inorder to evaluate the effectiveness of the strengthening actionobtained from the wiping-up procedure and the resultant spatialadjustment of the mounted filamerit, comparative tests on regularproduct lamps and lamps employing the improved mount construction wereconducted. The tests consisted of operating the lamps at of their designvoltage'in a horizontal position from sockets mounted on ahorizontally-disposed five pound steel plate which was droppedvertically through a distance of two inches thus simulating the hotshockconditions which prevail when the lamp receives a sudden impact whilethe filament is energized. -The foregoing schedule was repeated atone-second intervals with the lamps burning continuously until a totalof fifty impacts were successively applied to the lamps at which pointthe test was terminated. At the end of each drop the number of lampswhich failed were recorded so that the percent failures versus thenumber of impacts applied could easily be determined.

In the graph shown in Fig. 6, the percent failures after each drop areplotted along the ordinate While the number of impacts is plotted alongthe abscissa so that a so-called mortality curve for each lamp \type isshown. Two groups of twenty lamps each of identical structure andmanufacture, except for the configuration of the filaments, werecomparatively tested on three different occasions and the data averagedso that the figures in the graph represent the mean values derived fromsixty lamps of each type. As indicated by the curve A, the first regularproduct lamp failed after the seventh drop of the plate whereas thefirst lamp embodying the new construction, represented by curve B, didnot fail until after the twenty-third drop or more than three times thenumber of drops required to make the first regular product lamp fail.After the first failure occurred the rate of deteriorationof thefilaments in the remaining lamps, as evidenced by the rate at which thelamps subsequently failed and the generally parallel relationship ofcurves A and B, was approximately the same for each of the lamp types sothat at the conclusion of the test 60% of the lamps with regular orstandard construction had failed Whereas only 30% of the lamps with theimproved filament shape were inoperative. Hence, the introduction of apredetermined contour and strain pattern in the mounted filament inaccordance with the principles of the invention contrary to allexpectations efiected over a 300% improvement in the life span of theinitia' failure or-weakest-lamp mediate supporting members.

'5 in any given lot and a 100% improvement in the overall strengthquality of the lamps under sustained shock conditions.

As shown in Fig. 7, the invention may also be utilized in a so-calledC2F miniature lamp mount assembly 16a which comprises the usual pair ofspaced lead wires 20a and 22a, an insulator 18a, and two supportingmembers 44 and 46 disposed to support intermediate portions of arelatively longer filament 24a, as compared to that employed in the 02Vtype mount illustrated in Figs. 2 and 3, so that a generally rectangularfilament configuration is obtained. The filament end sections 28a inwardof the leads 20a and 22a are bent upwardly from their normallytransverse relation with the leads as heretofore explained in connectionwith the above-described embodiment of the invention to efiectsubstantially the same contour, strain pattern, and rigidification ofthe unsupported end spans of the filament proper set forth above.

The invention is equally applicable to stem-type mount assemblies 16b ofthe character illustrated in Fig. 8 and customarily employed in largerlamps and to other butttype mount assemblies, such as the so-called 02R.mount 16c shown in Fig. 9, wherein a shorter filament 24c is employedand suspended in toto on a pair of leads 20c and 22c by its end portions28c without the use of inter- In the former type mount construction theusual stem tube 50 having a fused end portion or press through which theleads 20b and 22b are sealed and a higher-wattage coiled filament 24b ofconsiderable length are employed which filament is anchored by its endsections 28b and intermediately coupled to a plurality of supportmembers 48 of appropriate length to provide a generally M-shaped lightsource, commonly referred to in the art as a C13 mount.

It will thus be obvious from the foregoing that the objects of theinvention have been achieved insofar as an improved filament mountconstruction and method of filament mounting for incandescent lamps areprovided whereby the rigidification resulting from the permanentdeformation and resultant straining of the mounted filament isadvantageously utilized to greatly improve the mechanical strength ofthe filament and the life quality of the lamp as a whole whichimprovement was not only entirely unexpected but is exceedinglyconvenient and inexpensive to attain.

Although one preferred and several alternative embodiments of theinvention have been described in accord- 6 ance with the patentstatutes, it will be understood that further modifications andvariations may be made without departing from the spirit and scope ofthe invention as defined in the appended claims.

I claim:

1. An electric lamp comprising, an envelope, a pair of lead wires sealedthrough and extending into said envelope, and a filament mounted on saidlead wires, said filament having a bend in each of its ends inward fromthe connecting portions of said lead wires that displaces the adjoiningunsupported section of said filament from its as-mounted configurationand permanently imparts thereto a configuration and a strain thatrigidifies and mechanically strengthens said unsupported filamentsection.

2. An electric lamp comprising, an envelope, a pair of lead wires sealedthrough and extending into said envelope, and a filament mounted on saidlead wires, said filament having generally straight end sectionsfastened to the ends of said lead wires and initially disposed intransverse relationship therewith, each of the straight end sections ofsaid filament inward from the connecting ends of said lead having a bendtherein that displaces the adjoining unsupported sections of saidfilament from their as-mounted configuration into a configuration thatrigidifies and mechanically strengthens unsupported filament sectionsand renders them less susceptible to sag.

3. A filament mounting comprising, a lead wire, and a coiled filamenthaving an uncoiled generally straight end section that is fastened tosaid lead wire in transverse relationship therewith, said filament endsection at a point inward from said lead wire having a bend therein ofsuch character that the innermost portion of said filament end sectionis displaced from its as-mounted transverse position toward parallelismwith the connecting part of said lead wire, thereby stressing theadjoining coiled body portion of said filament and imparting arigidifying con figuration thereto that renders it less susceptible tosag.

' References Cited in the file of this patent UNITED STATES PATENTS1,023,357 Beckwith Apr. 16, 1912 1,869,559 Gustin Aug. 2, 1932 2,214,974Scott Sept. 17, 1940 2,542,326 Greiner Feb. 20, 1951 2,716,714 Adams eta1. Aug. 30, 1955

